The Coastal & Marine Conservation Lecture Series is open to the public and occurs on the second Thursday of each month in the Florida State University Coastal & Marine Laboratory Auditorium.

“Declining Flows and Levels in the Apalachicola River and Effects on Floodplain Habitats” is the topic of the lecture set for Thursday, August 13, from 7 to 9 p.m. ET. Helen M. Light, U.S. Geological Survey, retired, will be the featured speaker. Light refreshments will be served after the lecture.

Apalachicola River levels have been declining for more than 50 years, with consequences to forests and streams throughout its extensive floodplain. Over the last three decades, the composition of floodplain forests has shifted to a drier mix of species, and further changes toward drier species could continue for many more decades.

Swamp species (water tupelo, Ogeechee tupelo, bald cypress, and Carolina ash) have declined in density, with approximately 3.3 million fewer swamp trees estimated in a 2004-06 study than were reported in studies from 1976 to 1979. Some low bottomland hardwoods such as overcup oak and green ash have also declined in numbers in bottomland hardwood forests, while drier species such as water oak and hackberry have become more numerous.

Floodplain streams, sloughs, and lakes are disconnected from the main river channel more often and for longer durations than 50 years ago, substantially decreasing offstream habitat for fishes, mussels, and other aquatic animals. Decreased flows have caused increased salinity in over 95 miles of streams in the lower tidal reach (tributaries and distributaries in the floodplain and main river channel).

Declines in river flows and levels have been greatest in spring and summer, which are the most important seasons for biological processes such as tree growth and fish spawning. Since 1975, there has been less flow in spring and summer as a result of water use, flow regulation, reservoir evaporation, and changes in rainfall patterns in the basin upstream. These declines in flow have exacerbated earlier water-level declines that were caused by channel erosion from engineering works begun in the 1950s (dam construction and navigation improvements such as river straightening, dredging, and wood-debris removal).

The Florida State University Coastal and Marine Laboratory is located at 3618 Highway 98 in St. Teresa (between Carrabelle and Crawfordville).